Freshly extracted citrus juice is subjected to a concentration step to store and preserve the juice for year-round consumption. Evaporation removes water from the fresh juice, and organic flavor and aroma compounds are removed with the vapor stream. The vapor stream condenses into a concentrated two-phase system. The water phase is referred to as "aqueous essence" and the oil phase is referred to as "essence oil".
Aqueous essence consists primarily of water, along with amounts of organic compounds such as low molecular weight alcohols (e.g., ethanol), aldehydes and esters. The essence is often added back to the concentrated juice to improve its flavor. However, aqueous essence obtained in the above-described method contains some organic compounds, especially components from peel oil, which impart off-flavors to the juice as well as those which impart good flavors. These off-flavors in the aqueous essence as produced by the concentration step then limit the amount of essence which can be added back to juice, in turn limiting concentrations of the good flavors from the essence which can be formulated in the final juice. Therefore, there is a need for improved aqueous essences containing high concentrations of good flavor compounds and fewer off-flavor compounds.
Several references disclose the use of activated carbon to enhance the flavors of fruit juices. For example, U.S. Pat. No. 3,071,474, issued to Gross (1963) discloses a process for the recovery of volatile flavoring compounds normally lost during fruit juice processing. The volatile flavors are trapped by adsorbing them on a suitable adsorbent such as activated charcoal. For example, the charcoal can be placed in the vapor line of a vacuum evaporator used to concentrate fruit juices. The charcoal picks up the volatile flavors while permitting the water vapor to pass on through to be condensed in the usual manner. Compounds of lower boiling points and lower molecular weight can be released from the activated charcoal by the use of a solvent such as an ether or hydrocarbon, and the flavors can then be added back to the juice. Example IV of the patent discloses an orange juice made according to the process.
U.S. Pat. No. 3,418,134, issued to Rooker (1968) discloses a process for adsorbing released volatile aromatics on activated charcoal prior to their deterioration in the preparation of concentrates from coffee, tea or cocoa. The process can also be used to adsorb volatile-containing aromatics released during conventional processing of a natural fruit product, such as the production of a fruit concentrate. The adsorbed aromatics are extracted from the charcoal by a solvent such as one of the chlorofluoromethanes and then added back to the juice.
U.S. Pat. No. 2,773,774, issued to McCarthy et al. (1956) discloses a process in which fruit juice is concentrated by evaporation of water therefrom at low temperatures under vacuum, and volatile flavoring materials are recovered from the vaporized water and returned to the concentrated juice. The process is particularly suited for citrus juices such as orange juice. The flavoring materials vaporized with the water in the concentration process are substantially all separated from the water by adsorption on a solid adsorbent such as activated carbon, particularly activated charcoal. The flavoring materials are steam stripped from the charcoal and returned to the juice.
Hassler, Purification with Activated Carbon, Chemical Publishing Co., Inc., New York, NY, pages 50, 106, 282-283, and 319-321 (1974), discloses that activated carbon can be used to decolorize fruit juices such as cherry juice, and to remove unpleasant taste caused by fermentation or other contamination from fruit juices such as pineapple juice.
In the Gross, Rooker and McCarthy et al. processes the solid adsorbent is used to adsorb volatile compounds from a vapor, not from a liquid as in the present invention. The volatile compounds of the prior art processes are the very high volatiles that are lost during evaporation, not compounds such as ethyl butyrate and hexanal. The Gross, Rooker and McCarthy et al. processes would not produce good fractionation of aqueous essence organic compounds.
Further, the use of solvents as in the Gross and Rooker patents has drawbacks because the solvents must be introduced from outside the process, resulting in added expense and the loss of an "all natural" product. The solvents are generally not food approved, and it is very difficult to remove all the excess solvent, usually by an added distillation step. None of the references suggests using citrus essence itself as the solvent, as in the present invention.
Aqueous essence is generally fractionated industrially by thermal distillation. This method can remove many off-notes, especially heavier compounds such as linalool. However, some off notes are difficult to remove by distillation. For example, ethyl butyrate and hexanal are difficult to separate because their boiling points are very similar. Hexanal removal is of particular importance, due to its negative flavor impact at higher concentrations.
Good analytical scale fractionation of chemical compounds can sometimes be obtained by using various forms of chromatography. Elution chromatography is a method commonly used for such analytical separations. In Snyder and Kirkland, Introduction to Modern Liquid Chromatography, 2nd Ed., John Wiley & Sons, Inc., NY, p. 15 (1979) descriptions are given of various forms of the method. The method employs two steps: first, the organic mixture of interest, dissolved in an external solvent, is loaded (adsorbed) onto the front end of a chromatographic bed (column). Second, another external solvent is moved through the column. The physical properties of the bed are chosen such that the compounds, while dissolved in the second solvent, have different affinities one from another for the bed. Also, the second solvent is chosen for the capability to dislodge the compounds from the bed. In this way the flowing solvent causes compounds to move down the bed at different rates. With a sufficiently long bed, compounds of different affinities can be completely separated one from the other in chromatographic "peaks". By collecting individual column effluent fractions containing only the "peaks" of interest, individual compounds can be separated.
While elution chromatography is effective for analytical chemistry and is a well developed technology, especially for small scale separations, the approach has disadvantages for larger scale operations needed to produce quantities of various materials for industrial use. First, an isocratic elution process (constant composition solvent) always dilutes the compounds with an unwanted solvent, frequently to levels much lower than the concentration of the compounds in the first loading step This is inherent in the isocratic elution process, because a significant amount of solvent is used to move compounds down the bed and away from one another. Gradient elution (solvent composition is gradually changed) can be used to maintain or increase concentrations, but this introduces additional unwanted solvent and is generally not appropriate for the type of operations described in this patent.
As a consequence, individual flavors produced by isocratic elution chromatography usually are heavily diluted and are not useful as produced. The dilute flavors obtained from elution usually must be thermally concentrated before use. The second disadvantage is the frequent requirement to completely remove the external elution solvent to produce an acceptable product.
An approach more amenable to large scale operation is frontal chromatographic separation. In Helfferich and Klein, Multicomponent Chromatography, Theory of Interference, Marcel Dekker, NY, p. 170-173 (1970) the method is described. In this method the adsorbent bed is first presaturated with solvent. Then, the flow is begun to the column of the organic mixture to be separated and the effluent from the bed is captured in fractions. As the mixture proceeds down the bed the component with the lowest affinity for the bed moves fastest down the bed and exits first. This first wave is a pure component. Following the first wave is a second corresponding to the component with the second lowest affinity for the fixed bed. This second wave also contains some of the first component. Similarly, the third wave contains the component with the third lowest affinity, as well as some of the first two components. This process can be continued until all components have broken through. At this point the liquid exiting the bed has the same composition as the column feed.
At breakthrough of the first component, i.e., the lowest affinity component, its concentration in the effluent is at least equal to, but often greater than its original concentration in the feed. The same is true for all components as they breakthrough in the effluent. Fractions are carefully collected and the process is continued until all components have individually broken through. In practice we seldom collect all fractions, because to obtain a useful separation the flow is stopped just as an undesirable component begins to break through into the effluent. At this point a significant portion of the acceptable, lower affinity components have passed through the bed and are contained in the effluent.
The frontal chromatographic separation method can be summarized as a process for splitting off a group of low affinity compounds from another group of high affinity compounds. Obtaining a pure compound with the solvent is not possible, except for the first breakthrough compound. The significant disadvantage of this method is the relatively poor separation selectivity between individual compounds.
Displacement chromatography, a more selective fractionation method, is sometimes used for larger scale separations. Frenz and Horvath, High Performance Displacement Chromatography: Calculation and Experimental Verification of Zone Development, AICHE J., 31, p. 400 (1985), describe this method and discuss how very sharp fronts can be obtained. This method employs two setups. First, the organic mixture of interest, dissolved in a solvent, is loaded onto the front end of the chromatographic column. The procedure is similar to the first part of the elution process, except that a larger portion (for example, one tenth to one half of the column) is loaded with the organic mixture. Second, a displacer with solvent is introduced into the column and permitted to slowly flow through the bed. The primary characteristic of the displacer is that it has a greater affinity for the bed than any of the components to be fractionated. As the displacer flows through the bed all components of lower affinity are pushed ahead of the displacer. With a sufficiently long bed the organic mixture resolves into a series of pure components in a sequence corresponding to the affinity sequence of the compounds. (Except, compounds with equal affinities will not separate one from the other.) The first component to emerge will be the species with the lowest affinity and will be a pure component in solvent. Immediately following will be the next lowest affinity component, also as a pure component in solvent. The third lowest affinity component emerges and so on until the displacer emerges. All components will be pure components in solvent, except for the crossover between adjacent compounds caused by axial dispersion or mass transfer resistance. Usually the bed is initially loaded with sufficient material that individual pure compounds can be obtained if desired.
The advantage of this process is that pure components can be obtained or individual negative flavors removed at will. Another advantage is the maintenance or sometimes increase in the concentration of components relative to the feed composition. This obviates the need for an expensive and complex concentration step after the fractionation.
The primary disadvantage of displacement chromatography is the difficulty in finding a suitable displacer. An ethanol/water system is a satisfactory eluent for an orange essence system, but it does not displace the flavors of primary interest. In a food system a natural material, preferably from the system itself, is most desirable. Unless the displacer is low cost, it must be recovered and recycled, usually an expensive route.
None of these references or the methods known to the art provide a simple, cost-efficient process with high recovery of valuable flavors while finely fractionating aqueous essences, and without thermal degradation. (These are requirements for a commercial process.) In particular, none provides a method for making improved citrus essences that have a high concentration of the good flavor compounds ethyl butyrate, ethyl acetate, and acetaldehyde, while containing low amounts of off-flavor compounds such as hexanal, linalool, and alpha-terpineol.
Therefore, it is an objective of the present invention to provide a process for making improved citrus aqueous essences that are high in good flavor compounds and low in off-flavor compounds, while maintaining high recovery of the good flavor compounds. Also, the process does not use external solvents, does not use a displacer, and does not use thermal distillation.
It is another object of the present invention to make the improved aqueous essences by a process involving passage of aqueous essence blends through a solid adsorbent such as activated carbon.
These and other objects of the present invention will become evident from the disclosure herein.